[RFC V1 09/16] arm64/mm: Route all pgtable reads via ptdesc_get()

[Anshuman Khandual]

Define arm64 platform specific implementations for new pXdp_get() helpers.
These resolve into READ_ONCE(), thus ensuring required single copy atomic
semantics for the page table entry reads.

In future this infrastructure can be used for D128 to maintain single copy
atomicity semantics with inline asm blocks.

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.org>
Cc: Ryan Roberts <ryan.roberts at arm.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 arch/arm64/include/asm/pgtable.h | 28 +++++++++++++++++++++++++++-
 1 file changed, 27 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
index 257af1c3015d..804ef49aea88 100644
--- a/arch/arm64/include/asm/pgtable.h
+++ b/arch/arm64/include/asm/pgtable.h
@@ -84,6 +84,32 @@ static inline void arch_leave_lazy_mmu_mode(void)
 	arch_flush_lazy_mmu_mode();
 }
 
+#define ptdesc_get(x)		READ_ONCE(x)
+
+#define pmdp_get pmdp_get
+static inline pmd_t pmdp_get(pmd_t *pmdp)
+{
+	return ptdesc_get(*pmdp);
+}
+
+#define pudp_get pudp_get
+static inline pud_t pudp_get(pud_t *pudp)
+{
+	return ptdesc_get(*pudp);
+}
+
+#define p4dp_get p4dp_get
+static inline p4d_t p4dp_get(p4d_t *p4dp)
+{
+	return ptdesc_get(*p4dp);
+}
+
+#define pgdp_get pgdp_get
+static inline pgd_t pgdp_get(pgd_t *pgdp)
+{
+	return ptdesc_get(*pgdp);
+}
+
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 #define __HAVE_ARCH_FLUSH_PMD_TLB_RANGE
 
@@ -384,7 +410,7 @@ static inline void __set_pte(pte_t *ptep, pte_t pte)
 
 static inline pte_t __ptep_get(pte_t *ptep)
 {
-	return READ_ONCE(*ptep);
+	return ptdesc_get(*ptep);
 }
 
 extern void __sync_icache_dcache(pte_t pteval);
-- 
2.43.0